Breath Acetone Meters

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The breath acetone meters I've tested in detail.
Acetone is produced when your body is burning fat, and this can be measured in your breath. There are now a growing number of options for measuring your breath acetone. The devices vary wildly in price, and I've found some of the cheaper options can be quite effective. In all cases, how you breathe when taking a measurement is critical to getting a consistent and accurate reading. Overall, I found that measuring breath acetone to be far more convenient, and far more useful than measuring blood ketone levels. Measuring breath acetone is vastly cheaper than blood tests, and obviously less painful. This allowed me to check my ketone levels throughout the day, enabling me to find more detailed information about how my body reacts to food and exercise.
  • The Ketonix is an FDA approved device that is designed specifically as a breath acetone meter. This is the only device that will give you an acetone reading in Parts Per Million, but is expensive and I found it to be cumbersome to use and I've experienced more erroneous readings than with cheaper devices.
  • A cheap breathalyzer can be used as an improvised breath acetone meter. While these devices are intended to measure alcohol intoxication through breast measurement, the cheaper devices also detect acetone. This means you have to get a cheap, low quality breathalyzer, as the better devices will filter out any acetone. (I like the Greenwon AT6000, [1]).
  • There's another dedicated breath acetone meter called Ketometer. It's cheaper than the Ketonix, but more expensive than a cheap breathalyzer.
  • LEVL is a remarkably expensive device for measuring breath acetone, and it requires an ongoing subscription. At the time of writing, it's$699 + $49/month, which is too expensive for me to consider. One interesting note is that it comes with a calibration gas, something I've not seen with any other device. LEVL.
  • There is a single use breath acetone test launched by Metron, but it's unclear if this is still available options. The cost of around $3/test makes it even more expensive than blood BOHB testing, which is generally considered the gold standard. Metron.

1 Ketonix

The Ketonix is designed to be a breath acetone meter for use with the Ketogenic Diet. While it's designed specifically for acetone, the documentation does mention that it will pick up alcohol in your breath as well, so it's similar to a cheap breathalyzer in that sense. A number of users have complained about inconsistent readings, and while I suspect that most of this is due to breathing patterns, I've also had some issues. The Ketonix requires a long and variable warm up time, usually between 2 and 10 minutes, plus needing to be powered up for 2 minutes after taking a reading, making it cumbersome.

1.1 Testing The Ketonix

The Ketonix feels like a medical grade device, made out of high quality materials but lacking the polish of a consumer grade device. If it were a choice between the Ketonix and blood ketone testing, I'd highly recommend the Ketonix as a vastly superior solution. However, having compared it to the cheap breathalyzers, I'd recommend buying the cheap breathalyzers. The Ketonix is obviously the best choice for clinical or research settings, but the only significant advantage the Ketonix has over the breathalyzer for casual use is its ability to read low levels of acetone.

  • Start up. In my testing, I found the warm up period really annoying. Having to wait 2 to 10 minutes for it to start up and get up to temperature makes it impossible to use to check your acetone levels during a run, and at other times it makes the test excessively time consuming. The manufacturer doesn't recommend leaving it plugged in all the time, so that's not a solution.
  • Tethering. The Ketonix can be used without being connected to a computer, but it will just flash a colored light to give you an idea of the acetone range. To get a numeric value you have to have it plugged into a computer (the latest version supports a smartphone via Bluetooth.)
  • Erroneous Readings. Using the rebreathing technique (breathing into a bag five times) generally gave me highly repeatable values, but about 1 in 20 readings were erroneous. I've not been able to work out what the underlying cause of these erroneous readings might be. The initial indication of an erroneous reading is that it's out of line with all the other tests, such as urinalysis, blood BOHB, the other acetone breathalyzers, and my general expectation. I typically find that simply repeating the test gives me a second result that's extremely close to the initial erroneous reading. If I disconnect the Ketonix and restart the software (sometimes a couple of times) the reading will dramatically change to be in line with expectations, and the new readings are quite repeatable. It seems like the Ketonix has a bad baseline or calibration, but I don't need to recalibrate to resolve the issue. I contacted Ketonix support and they were very responsive, but unable to offer any suggestions unless I could come up with a repeatable process for replicating of the error.
  • Correlations. I found the Ketonix results were surprisingly well correlated with blood ketone testing. It's critical to remember that breath acetone and blood BOHB are testing two different Ketones, so you'd expect some difference. The main ketone is Acetoacetic acid (AcAc) which can be metabolized by the body, and both of blood and breath testing are measuring "secondary ketones". BOHB can be thought of as a ketone storage bank, and acetone can be thought of as a side effect of AcAc. The relationship between BOHB and AcAc can vary widely, from 1:1 up to 10:1, making AcAc a better option than BOHB. The research I've found indicates that Acetone and AcAc generally have a stable relationship. Ketonix suggests a value of 40 to 80 PPM indicates a statue of nutritional ketosis, though I found my levels were far lower, with 10-40 being ketosis.
    My BOHB blood tests against Ketonix Acetone PPM

1.2 Ketonix Versions

There are several generations of Ketonix:

  • Original. The first generation glowed in three different colors to indicate your breath acetone level. While the original version connects via USB, it doesn't appear that there is any data transfer.
  • Ketonix 2015. This generation that provides an acetone measure as a number between 0-100. The 2015 version was available in red or blue, each with a slightly different preloaded configuration.
  • Ketonix 2016. With this update, the breath acetone level is given as PPM rather than an arbitrary number.
  • Ketonix 2017. The latest version uses Bluetooth to connect to a smart phone app in addition to the earlier USB integration. There's an upgrade adapter for earlier versions to use Bluetooth.

2 Cheap Breathalyzers

A good quality breathalyzer will only measure breath alcohol content, screening out any acetone that's present. However, the cheaper breathalyzers that use a simple silicon sensor don't to distinguish between alcohol and acetone. This makes them an interesting option for checking breath ketones, and I've tested several different types. One obvious conclusion is that because you're buying a remarkably cheap device, quality is rather poor. I had one device that just gave random readings, even with the rebreathing technique mentioned below. I've tested these cheap breathalyzers and found a good correlation between them and Ketonix as well as with blood ketone testing. Here are some suggested devices:

  • Greenwon AT6000. This small handheld device shows Blood Alcohol Content (BAC) to three decimal places. That's nice to have, as BAC values I've measured are typically in the range 0 to 0.13, so the AT6000 provides an extra significant digit. If you're BAC value is above 0.05, it will be loudly and repeatedly to warn you that you're too drunk to drive, which is really annoying if you're stone cold sober. All these cheap breathalyzers have a warm-up period for their sensor, and the AT6000 counts down from 100, taking about 20 seconds. The AT6000 is sold by various companies on Amazon, including [2].
  • Greenwon Keyring. This is a smaller version of the AT6000, though the size difference isn't all that great. It only provides BAC values to two decimal places, and it warms up in 10 seconds. It's a little cheaper than the AT6000, and its beeps are really quiet, something that I appreciate.
  • AlcoHAWK Slim. The shape of the AlcoHAWK works well for me, as it will slip into the pocket of my Race Ready Shorts and Tights, making it a little easier to use while out for a run. It only provides two decimal places, and a fairly soft beep. It has a long warmup time, and the warmup time is variable between 20 and 40 seconds, which is annoying. The mouthpiece folds down, which makes carrying easier.

2.1 Testing The Breathalyzers

I tested these cheap breathalyzers for about a month, comparing them to occasional blood ketone levels as well as the Ketonix. I have been impressed by how effective both the Greenwon breathalyzers are at measuring acetone levels. Using the rebreathing technique provides a little more consistency, but it's not critical if you're just after a reasonable estimate of your ketone levels. I have found that the Greenwon sensors tend to read zero if your ketone levels are quite low (mostly below 3 PPM). On the whole, I much prefer using these cheap breathalyzers to the vastly more expensive Ketonix. The cheap breathalyzers warm up in a fraction of the time, and if you're doing the rebreathing then the warm-up time is about the same as the multiple breaths you need before taking a reading. These cheap breathalyzers also have a built-in a display and are battery powered, so they're completely portable. There also cheap enough to have two devices to cross check. I'd recommend getting both the key ring and the AT6000.

3 Converting Ketone Values

My testing has produced some initial indications on how blood BOHB and breath acetones might interrelate. This is useful as most research provides blood BOHB values, and the definition of "nutritional ketosis" is typically given in BOHB concentrations. My readings suggest that dividing Ketonix PPM by 12 is roughly my BOHB concentration, which means that the threshold of Ketone Levels of 0.5 mmol/L BOHB would be about 6 PPM. My readings suggest that multiplying breathalyzer BAC by 40 is roughly my BOHB level, meaning 0.5 mmol/L BOHB would be about 0.012% BAC. Dividing my Ketonix PPM by 450 gives my breathalyzer BAC.

4 Ketometer

The Ketometer is much cheaper than the Ketonix, but it has rather more of a prototype vibe to it. The Ketometer doesn't provide a PPM reading, just a relative value, and there's no software interface or indication of calibration. I think the price point for the Ketometer is a little wrong; if I'm willing to pay for the Ketometer, I'd rather pay a little more and get to the Ketonix. If I don't want the accuracy and software support of the Ketonix, then I'd stick with a cheap breathalyzer. More at

5 Breathing Patterns

Acetone is exchanged mostly in the airways, not the part of your lungs that exchange carbon dioxide and oxygen. This means that the way you breathe into a breath acetone meter will have a big impact on the acetone concentration in your breath:

  • A normal, resting breath will result in only about two thirds the maximum acetone concentration.
  • A full breath, breathing in deeply and fully exhaling will result in ~85% of maximum acetone concentration but only at the end of the breath. For cheap breathalyzers, they often don't measure the full breath.
  • Breathing in and out of a bag for six breaths results in the maximum acetone concentration and the best repeatability. Of course, this is the most uncomfortable method.
  • Breath holding, even for more than 60 seconds, has no impact on breath acetone concentration.

6 See Also